The present invention relates to a magnetic disk drive and, more particularly, to a technology which is effectively applicable to the transmission line structure to be mounted on the suspension for transmission of writing-reading signals to and from the magnetic head. The magnetic disk drive which is designed to write and read a large quantity of data in a limited space within a short time needs a technology to increase the recording density, a technology to increase the rate of data transmission, and a technology to increase the frequency for writing and reading. There is a type of magnetic disk drive meeting these requirements in which the line for transmission of writing and reading signals to and from the magnetic head is formed by printing on the suspension. This transmission line is composed of a pair of conductors for writing and a pair of conductors for reading. The conductors of both the writing line and reading line have lower conductors, with an insulating layer interposed between them. In the conventional transmission line as mentioned above, the conductors for writing line and reading line are formed from copper which is about 15 μm thick, the lower conductors are formed from stainless steel which is about 25 μm thick, and the insulating layer is formed from polyimide resin which is about 10 μm thick.
According to Japanese Patent Laid-open No. 2002-237016, the transmission line is mounted on the suspension in such a way that the FPC (flexible printed circuit) constituting the transmission line has a sheet member closely attached to the back thereof, said sheet having a higher thermal conductivity than stainless steel from which the suspension is formed. This sheet member may be formed from aluminum as well as copper, and its maximum thickness is about 500 μm.